iMac 5k inconsistent Framerates

[ENAI]

The inconsistent performance seems very much like a throttling problem, which is almost unavoidable on most newer iMacs and Macbooks. Basically, the cooling in those computers is so minimal that it can't keep up with the components. This causes the components in question forcefully slow down as a safety measure when they get to dangerous temperatures. There isn't really much you can do about it other than come up with a custom cooling solution, like a desk fan next to the cooling vents of the Mac (or, you know, not pushing the computer so hard). Also, to make sure that this is exactly the problem, you could use something like MSI Afterburner or similar that shows you the temps and clocks of your CPU. If you see a sudden drop in the clocks when the CPU hits somewhere between 80 and 100 Celsius (I don't know the Mac's thermal ceiling exactly), then you know it's thermal throttling.